As the integration density of LSIs increases, the circuit line widths of semiconductor devices become narrower year by year. Forming a desired circuit pattern on a semiconductor device involves using a technique in which a high-precision original pattern (also referred to as a mask, or particularly referred to as a reticule if it is used in a stepper or scanner) formed on a quartz member is transferred in a reduced form onto a wafer using a step-and-repeat exposure system. The high-precision original pattern is written by an electron beam writing apparatus using a so-called electron beam lithography technique.
In the electron beam writing apparatus, writing data input from the outside is distributed in units of predetermined calculation regions among a plurality of calculators, which concurrently perform data conversion operations to reduce data processing time. After the concurrent data conversion, the resulting data is temporarily input to a transfer processing device, and then transferred to a deflection control circuit in writing order. The deflection control circuit determines the amount of deflection of a beam on the basis of the transferred data, and deflects the beam to irradiate a mask substrate. The mask substrate is placed on a stage that continuously moves.
If data transfer from the transfer processing device to the deflection control circuit is too slow to prevent interruption of data for a region that is being written to, the writing process is stopped. Then, a so-called recovery process is performed, which involves returning the stage to a position where writing has been accurately performed and then resuming the writing process after writing data is transferred.
As optical lithography technology develops and the wavelengths shorten because of the use of EUV, the number of electron beam shots required for mask writing increases. At the same time, to ensure line width precision required for narrowing the line widths, the resist sensitivity is lowered and the dose is increased to reduce shot noise and pattern edge roughness. The writing time increases as the number of shots and the dose increase. Increasing the current density is under consideration to shorten the writing time.
However, in an attempt to emit an increased amount of irradiation energy in a short time in the form of a higher-density electron beam, a phenomenon of so-called resist heating occurs, in which an increase in substrate temperature causes a change in resist sensitivity and degrades the line width precision. To solve this problem, a technique has been proposed, which involves calculating, for each minimum deflection region in deflection regions, a representative temperature of the minimum deflection region based on heat transfer from other minimum deflection regions that have been previously written to, and modulating a dose using the representative temperature (see, e.g., Japanese Unexamined Patent Application Publication No. 2012-69675).
If a recovery process, such as that described above, occurs during the writing process performed using the dose modulated by taking into account the heat transfer from other regions, the substrate temperature drops while the stage position is being returned. Therefore, when, after the writing operation is resumed, writing is performed using the dose that takes into account the heat transfer, desired line width precision cannot be achieved.